Embodiments described herein relate generally to valves that control a flow of fluid, and more particularly, to valves for controlling the flow of fluid in engine exhaust gas recirculation (EGR) systems.
Engine exhaust gas recirculation is a known technique for reducing oxides of nitrogen in products of combustion that are exhausted from an internal combustion engine to the atmosphere. A typical EGR system comprises an EGR valve that is controlled in accordance with engine operating conditions to regulate the amount of engine exhaust gas that is recirculated to the intake flow entering the engine, so as to limit the combustion temperature, and further, to reduce the formation of oxides of nitrogen during combustion. To the extent that exhaust gas is introduced into the flow entering the engine, the exhaust gas displaces air that would otherwise enter the engine.
The EGR valve is the main emissions control component in the EGR system. The EGR valve is typically located at an intake manifold and is connected between an EGR conduit and the engine. Typically, the EGR valve has a housing that is inserted into an intake manifold pocket, and the EGR valve opens a small exhaust gas recirculation passageway between the EGR conduit and the intake manifold to allow a metered amount of exhaust fluid flow to the engine.
Different amounts of EGR fluid are provided at different engine operating conditions. At cruising, high-speed or mid-range acceleration, when combustion temperatures are very high, high EGR fluid flow is provided. At low speed and light load conditions, low EGR fluid flow is provided. At engine warm-up, transient, idle, or wide open throttle conditions, no EGR fluid flow is provided.
Typically, the flow of EGR fluid is controlled not only by the EGR control valve, but also by a separate modulator assembly. The modulator assembly typically uses the exhaust backpressure (which is proportional to engine load) to send a vacuum signal to control the EGR flow rate through the EGR valve to be generally proportional to the amount of load applied to the engine. A bypass valve can be used to divert excess EGR fluid flow around the EGR cooler during engine conditions where EGR fluid flow is low or not provided.